What is a photon? How is the energy of a photon related to its wavelength? Its frequency?

Electromagnetic radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays, and gamma rays. Sunlight is also a type of electromagnetic radiation called visible light.

Electromagnetic radiation can be described as a series of waves characterized by their wavelength (\( \lambda \)) and frequency (\(u\)). These waves can travel through the vacuum of space at a constant speed, denoted by \( c \), which is approximately 299,792 kilometers per second. The different types of electromagnetic radiation differ in their wavelengths and frequencies, which determines their energy and thus their effects on matter.

Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. In quantum mechanics, energy is quantized, meaning it can only occur in discrete amounts called quanta.

One of the revolutionary concepts that quantum mechanics introduces is the idea that particles can behave like waves and waves can behave like particles. This wave-particle duality is especially evident in the behavior of photons, which are packets of electromagnetic energy that exhibit both wave-like and particle-like properties.

Planck's constant (\( h \)) is a fundamental constant in quantum mechanics that has a value of approximately \( 6.6261 \times 10^{-34} \) Joule-seconds. It plays a crucial role in the quantization of energy and is named after the physicist Max Planck, who discovered it.

Planck's constant defines the size of the discrete packets of energy, or quanta, which we know as photons. In mathematical terms, Planck's constant bridges the gap between the wave-like and particle-like properties of energy. It is a key constant in the equations that define the energy of a photon based on its frequency and wavelength.

The wavelength (\( \lambda \)) and frequency (\(u\)) of electromagnetic radiation are inversely related to each other by the speed of light (\( c \)). This means that as the wavelength of light increases, its frequency decreases, and vice versa. The relationship is expressed by the equation \( c = \lambda \times u \).

Implications on Photon Energy

Given this relationship, we can understand the energy of a photon (\( E \)) in two ways: inversely proportional to its wavelength (\( E = \frac{hc}{\lambda} \)), and directly proportional to its frequency (\( E = hu \)). This duality is fascinating because it tells us that the energy contained in a photon of light is dependent on its characteristics as both a wave and a particle.